Public vs. Private IP Addresses: What’s the Difference?

Last updated: May 31, 2026

Every device that communicates over a network needs an IP address. But not all IP addresses serve the same purpose. Some addresses identify you on the global internet. Others exist only within the boundaries of your home or office network. The difference between these two types, public and private IP addresses, is one of the most fundamental concepts in networking.

You may have wondered why your router has one address and your laptop has a different one. Or why every device in your house seems to share the same IP when visiting a website. The answer lies in this public-versus-private distinction. A third category also exists. RFC 6598 reserves a special range for ISP carrier-grade NAT that is neither traditional private nor truly public. Most beginner articles skip it. We cover it here.

When network issues arise, understanding which address is involved is often the first step in a systematic troubleshooting approach.

What Is a Public IP Address?

A public IP address is a globally unique address assigned to your network by your ISP. It identifies your network on the internet. When you visit a website or send an email, the remote server sees your public IP as the source. Public IPs are internet-routable and visible to every service you connect to.

A public IP address is a globally unique address assigned to your network by your Internet Service Provider (ISP). It is the address that identifies your network on the internet. When you connect to a website or service, the remote server sees your public IP as the source.

Public IP addresses have several defining characteristics:

• Globally unique. No two devices on the public internet can share the same public IP address at the same time. Regional Internet Registries (RIRs) like ARIN, RIPE, and APNIC manage allocation to ensure uniqueness. A WHOIS lookup reveals which registry and ISP own any public block.
• Internet-routable. Routers across the internet know how to forward traffic to and from public IP addresses. They appear in global routing tables maintained by ISPs and backbone providers.
• Visible to remote servers. Every website, API, and online service you connect to can see your public IP address in the packet headers.
• Assigned by your ISP. You do not choose your public IP. Your ISP either assigns one dynamically each time your router connects (dynamic IP). Or provides a fixed one under a business or premium plan (static IP).

Most residential connections use dynamic public IPs, which may change periodically when your router reconnects. Businesses that host servers, run VPNs, or need consistent DNS records typically pay for static public IPs. These remain the same indefinitely.

How to Find Your Public IP

The quickest way to find your public IP address is to use a dedicated lookup tool. NetworkCheckr’s My IP Address tool shows your public IP instantly. For a detailed walkthrough of multiple methods, see our guide on how to find your public IP address.

From the command line, you can also query a public service:

curl ifconfig.me

This returns your public IP because the remote server (ifconfig.me) sees the source address of your request. After NAT, that source address is your router’s public IP. Protecting it with a firewall is important.

What Is a Private IP Address?

A private IP address is reserved for use within local networks. These addresses come from three ranges defined in RFC 1918 and are not routable on the internet. They let organizations reuse the same ranges internally, extending the effective IPv4 address space. Routers drop internet packets with private addresses.

A private IP address is an address reserved for use within local networks. These addresses are defined in RFC 1918 and are not routable on the public internet. Any router on the internet that encounters a packet with a private source or destination address will drop it.

Private addresses exist because IPv4 has only about 4.3 billion addresses total. Not enough for every device in the world to have its own public IP. RFC 1918 lets organizations reuse the same private ranges internally, massively extending the effective address space. Your home network can use 192.168.1.0/24, and so can your neighbor’s. There is no conflict because these addresses never appear on the public internet.

The Three Private IP Ranges

To plan subnets within these ranges, use our Subnet Calculator. It divides them into appropriately sized blocks. To expand a block into its address range, try the CIDR to IP Range tool. Private addressing is an IPv4 concept rooted in address scarcity. The picture changes with IPv6, which provides enough addresses to give every device a globally unique one.

The Often-Missed Fourth Range: 100.64.0.0/10 (CGNAT Shared Address Space)

Most beginner explainers stop at the three RFC 1918 ranges. There is a fourth, often overlooked range that has become critical to understanding modern networks.

RFC 6598, published in 2012, reserves 100.64.0.0/10 (the range from 100.64.0.0 to 100.127.255.255) as shared address space. Roughly 4.2 million addresses. It was sized to handle a metropolitan area as large as Greater Tokyo, the world’s largest metro region.

This range is not public. Routers on the internet will not forward it. But it is not private in the traditional RFC 1918 sense either. It is reserved specifically for use between subscriber routers and ISP carrier-grade NAT (CGNAT) infrastructure.

The practical implications for users behind CGNAT:

• Port forwarding usually does not work. Inbound traffic stops at the ISP’s NAT layer before reaching your router.
• Self-hosting becomes difficult. Running a game server, security camera, or website from home is blocked.
• Geolocation may be off. The CGNAT exit IP may be hundreds of miles from your actual location.
• IP-based bans hit multiple customers. A bad actor at another customer can get the shared public IP banned, affecting you too.

To detect CGNAT, compare two addresses. Your router’s WAN IP from the admin panel, and the public IP shown by our My IP Address tool. If they differ, or if the router WAN IP is in 100.64.0.0/10, you are behind CGNAT.

How NAT Connects Public and Private Addresses

NAT (Network Address Translation), defined in RFC 3022, bridges the gap between private and public IP addresses. Your router replaces each device’s private source address with the router’s public IP before traffic leaves the network. Response packets are routed back to the correct device using port mapping tables maintained by the router.

Network Address Translation (NAT) is the mechanism that bridges the gap between private and public IP addresses. Defined in RFC 3022, NAT allows devices with private addresses to communicate with the public internet. The router translates private source addresses to a public address at the network boundary.

Here is how a basic NAT flow works:

1. Your laptop (private IP 192.168.1.10) sends a request to a web server at 93.184.216.34.
2. The packet reaches your router. It replaces the private source address with the router’s public IP (for example, 203.0.113.45). It also assigns a unique source port number.
3. The web server receives the packet from 203.0.113.45 and sends its response back to that address.
4. Your router receives the response. It looks up the port mapping in its NAT table and forwards the packet to 192.168.1.10.

PAT: Port Address Translation

In practice, most home and small business routers use PAT (Port Address Translation), also called NAT overload. PAT allows multiple devices to share a single public IP by assigning each session a unique source port number. The router maintains a translation table:

Each row represents a different device on the local network. All share the single public IP 203.0.113.45. The router uses the unique external port number to route responses back to the correct internal device. For a deeper look at how port numbers work in networking, see our Port Number Reference.

Public vs Private IP Address: Side-by-Side Comparison

Six characteristics distinguish the two types: assignment authority, scope, uniqueness, routability, visibility, and example values. Public IPs are assigned by ISPs, globally unique, and visible to every internet service. Private IPs are assigned by your router, reused across millions of networks, and visible only on the local LAN.

The following table summarizes the key differences between public and private IP addresses:

How to Find Your Public and Private IP

Three methods find your public IP: a web lookup tool, the curl command line, or your router admin panel. Three commands find your private IP. ipconfig on Windows. ifconfig on macOS or Linux. Or ip addr show on newer Linux. Each method has its own use case.

Finding both your public and private IP addresses is a practical skill. It helps with troubleshooting, configuration, and security checks.

Finding Your Public IP

• Web tool. Visit NetworkCheckr’s My IP Address tool for an instant result.
• Command line. Run curl ifconfig.me or curl icanhazip.com in your terminal.
• Router admin panel. Log in to your router (commonly at 192.168.1.1) and look for the WAN or Internet status page. The router shows the public IP assigned by your ISP. If that WAN IP differs from what your IP lookup tool shows, your ISP is using CGNAT.

Finding Your Private IP

Windows:

ipconfig

Look for the IPv4 Address line under your active network adapter. It will show an address like 192.168.1.10 or 10.0.0.5.

macOS / Linux:

ifconfig

Find the inet entry under your active interface (usually en0 on macOS or eth0/wlan0 on Linux). On newer Linux distributions, you can also use ip addr show.

To see how your IP address looks in binary notation, try our IP to Binary Converter. It breaks down each octet into its 8-bit representation.

Why the Public vs Private IP Address Distinction Matters

The division is not just academic. It has real implications across four key areas. Security determines how your network is exposed to attacks. Network design depends on private address planning. IPv4 conservation is the reason private addressing exists at all. Troubleshooting becomes much faster when you know which address is involved.

The division between public and private addresses is not just academic. It has real implications across four key areas of networking.

Security

Your public IP is exposed to the internet and can be scanned by anyone. Attackers routinely sweep public IP ranges looking for open ports and vulnerable services. A properly configured firewall is your first line of defense. It controls which inbound connections are permitted and blocks everything else. Private IP addresses are shielded from direct internet access by the NAT boundary. But that does not mean they are inherently safe from internal threats.

Network Design

Designing a network requires careful planning of private address space. Choose the right RFC 1918 range, divide it into subnets, and assign addresses systematically. This prevents conflicts and makes the network easier to manage as it grows. Private addressing sits within the broader OSI model at Layer 3, the Network layer. This clarifies how routing and addressing decisions interact with other layers.

IPv4 Conservation

The entire reason private addressing and NAT exist is IPv4 address exhaustion. Only about 4.3 billion public IPv4 addresses are available globally. There simply are not enough public addresses for the billions of connected devices worldwide. Private addressing combined with NAT lets thousands of devices share a single public IP. The long-term solution is IPv6. IPv6 provides a virtually unlimited address supply. The transition is gradual and IPv4 remains heavily used.

Troubleshooting

When diagnosing connectivity problems, knowing whether the issue involves your public IP or your private IP narrows the problem significantly. If a DNS lookup fails, is it because the DNS server cannot reach your public IP? Or because your device’s private IP is misconfigured? Understanding how DNS works end to end helps trace the failure. If a reverse DNS lookup on your public IP returns unexpected results, the problem is with your ISP. Not your local network. Not your local network. Knowing which address is relevant at each stage saves time and prevents misdiagnosis.

Common Misconceptions

Three common misconceptions distort how people think about IP addresses. First, that private IPs are secret (they are not). Second, that NAT is a firewall (it is not). Third, that every device has its own public IP (it does not). Clearing these up makes practical decisions easier.

“My Private IP Is Secret”

Many people assume that because a private IP address is not routable on the internet, it must be confidential. In reality, knowing that someone’s device is at 192.168.1.10 tells you almost nothing useful. Millions of networks use that exact same address. Private IPs are not secret. They are simply not unique. The security benefit of private addressing comes from non-routability, not obscurity.

“NAT Is a Firewall”

NAT does provide a side effect of blocking unsolicited inbound connections. The router has no NAT table entry to know where to forward them. But NAT was designed for address translation, not security. It does not inspect packet contents, filter by protocol or application, or log suspicious activity. A proper firewall provides intentional, configurable, auditable security. NAT does not. Relying on NAT as your only protection leaves significant gaps.

“Every Device Has Its Own Public IP”

This is one of the most common misunderstandings. In a typical home network, your ISP assigns one public IP address to your router. Every device on your network, phone, laptop, smart TV, game console, shares that single public IP through NAT. Each device has its own private IP within the local network. But to the outside world, they all appear as the same address. Under CGNAT, that “public” IP is shared with other customers too.

Related Tools & Resources

NetworkCheckr offers complementary tools for IP address workflows. The My IP Address tool shows your current public IP. The Subnet Calculator handles CIDR math for both IPv4 and IPv6. Companion guides cover how to find your public IP, IP address formats, and the IPv4 vs IPv6 transition.

• My IP Address — check your current public IP with geolocation and ISP detail.
• How to Find Your Public IP Address — five methods plus CGNAT detection workflow.
• Subnet Calculator — CIDR math for IPv4 and IPv6 networks.
• CIDR to IP Range — expand a private CIDR block into its full address range.
• WHOIS Lookup — see which RIR and ISP own a given public IP block.
• IP to Binary Converter — convert IPv4 addresses between decimal, binary, and hex.
• IP Address Formats Explained — companion explainer on notation rules.
• IPv4 vs IPv6 — the protocol comparison and 2026 adoption stats.
• Subnetting Beginner’s Guide — start here if subnet math is unfamiliar.
• All NetworkCheckr Tools — the full set of free networking utilities.

Frequently Asked Questions

Seven questions cover the practical edge cases. What 192.168 addresses are. Whether someone can hack you using your public IP. How many private addresses exist. What VPNs change. Why all your devices share one public IP. What happens when IPv4 runs out. And how to detect whether you are behind CGNAT.